Anybody ever overhaul synths??

[wiz1der]

I have an old ARP Omni that has like stuck notes and other things. From researching on the web it is mostly cap replacement.

Is this pretty easy, just pull out the old ones while replacing with new ones one by one?

This forum is great!!

 

[Steve Jones]

The tanatalums on the trigger circuit of each key usually need to be replaced. I have used electrolytics successfully, if you can find small ones, they are cheaper than tantalums. Don't forget also to replace the tantalums in the power supply, and on each board where the 3 pin Molex power connector is.

 

[wiz1der]

O.k. i popped open my ARP OMNI model 2480 to start taking inventory on cap values, and I saw a place on the upper voicing board that looks like a terrorist bombed it!!





http://groupdiy.twin-x.com/displayimage.php?pid=126&fullsize=1

surprisingly the keyboard still makes sounds! not very good ones though.

I want to swap all these caps. SO,

for these tants, those are the blue ones right? Can i go with non-polarized electrolytics?

for the ceramic discs, I need to go ceramic monolithic dipped?

I am so confused and seeking some guidance from you experts out there.

I have a service manual on the way from schematics connection.

HELP please? thanks in advance.

http://groupdiy.twin-x.com/displayimage.php?pid=125&fullsize=1

other board.

also it looks as if someone replaced a few things in here, as one row of caps has an electro in the tant row.

 

[Steve Jones]

Yikes, something really went on that board. I will have a look in my service manual in an hour or 2 and see what was there. Don't replace the ceramic capacitors, there is no need, in 20 years of servicing synths I have never seen one fail. They probably used tantalums to save space back in the days before really small electrolytics, and in the keying circuit possibly too because of their lower leakage. you can see in the bottom picture someone has already put an electrolytic in at some point among the tantalums.

Those 2 on the power supply board need to be replaced right away, as for the rest, you can just buy new tantalums if you want, but they are expensive, or as I did with my Omni 2 just get normal polarized electrolytics with the same ratings as the tantalums and replace the lot. My machine played fine with electro's, so leakage in the trigger circuit seems not to bee an issue. Don't forget to put them in with the same polarity as the tantalums you remove.

As for the existing electrolytics, it might be good to replace the power supply filter caps, they would have copped a few spikes and surges over the last 25 years or so and would be a bit tired for sure.

 

[wiz1der]

[quote author="Steve Jones"]Those 2 on the power supply board need to be replaced right away.[/quote]

you mean the BIG orange ones?

[quote author="Steve Jones"]As for the existing electrolytics, it might be good to replace the power supply filter caps, they would have copped a few spikes and surges over the last 25 years or so and would be a bit tired for sure.[/quote]

which ones are these? I don't see any electrolytics on the p/s.

I appreciate your quick response, and having a look at your schematics for me. :thumb:

 

[alk509]

[quote author="wiz1der"]you mean the BIG orange ones?[/quote]

No, the two tantalums ones. Just replace them and you'll avoid some grief.

[quote author="wiz1der"]which ones are these? I don't see any electrolytics on the p/s.[/quote]

Errr... The two big orange ones are electros... Like Steve said, you might as well replace those too.

Peace,
Al.

 

[donnie7]

Would it be wise to replace any electrolytic caps in older synths? Units include Ensoniq ESQ-1, SQ-80, Roland D-50. Are there usually electrolytics on the output section?

 

[wiz1der]

[quote author="alk509"][quote author="wiz1der"]you mean the BIG orange ones?[/quote]

No, the two tantalums ones. Just replace them and you'll avoid some grief.

[quote author="wiz1der"]which ones are these? I don't see any electrolytics on the p/s.[/quote]

Errr... The two big orange ones are electros... Like Steve said, you might as well replace those too.

Peace,
Al.[/quote]

Is there anywhere online that will explain the different types of components, with illustrations? I got some studying to do.

 

[wiz1der]

O.K. after having so many projects going at once, I finally buckled down and replaced all these caps. This thing sounds wonderful EXCEPT:

In my bass section, all the keys are playing the same note, if you want to call it a note.

I am suspecting bad cd-40xx chips? Anybody with some expert advice on what I should check for?

I do have the schematics now.